Variable condenser



April 1930- 1.. A HAZELTINE 1,755,115

VARIABLE CONDENSER Original Filed April 3, 1925 2 Sheets-Sheet l @QT/a,

ATTORNEYS April 15, 1930. L. A. HAZELTINE 1,755,115

VARIABLE CONDENSER Original Filed April' 3, 1925 2-Sheets-$heet 2 147? zzZar ad 'watmenl' /fi/lsplac many ii- Z I a a326 [4 1 3 INVENTOR CI C Zea/'5 A. Hazel/inc B3 W ,Z M,

Patented Apr. 15, 1930 UNITED STATES PATENT OFFICE LOUI S ALAN HAZELTINE, OF HOIBOKEN, NEW JERSEY, ASSIGNOR TO HAZELTINE C013.- PORATION, A'CORPORATION OF DELAWARE VARIABLE connnnsna Original application filed April 3, 1925, Serial No. 20,484, and in Great Britain, Australia, and New Zealaml April 3, 1925. Divided and this application filed October 7, 1927. Serial No. 224,548.

This inventionrelates to radio amplifiers and radio receivers. v

The circuit arrangement for reception of radio signals which has produced excellent results because of its sensitivity and selectivity is that employing tuned radi0-frequency amplification in several stages, with elimination or neutralization of coupling between stages, as described in my United States Letters Patent No. 1,489,228, No. 1,533,858, No. 1,57 7 ,421, and No. 1,648,808. While receivers of this type have met with almost universal approval from users it has been recognized that it would be highly desirable to reduce the means for tuning to a single control, and fur ther to obviate the need of an external antenna.

Telephone transmitting stations employ undamped carrier currents, the oscillations of Y which have no decrement, so that the incoming signals can be received in closely coupled and sharply tuned circuits The employment of undamped carrier currents permitting the use of closely coupled and sharply tuned circuits has previously necessitated an individual control for each-of the several stages. This multiplicity of controls is due .to the fact that manufacturers have been unable, in prac tical construction, to produce coils and condensers with substantially no variation in electrical characteristics-a condition which must be met if a single control is to be employed for tuning a plurality of circuits exactly. \Vhere a common control was formerly provided to vary simultaneously the tuning of all the circuits of a radio receiver, the mentioned manufacturingvariations introduced wide inequalities, with resultant detuning in the respective stages throughout at least a portion of the intended operating range, or efl'ective frequency hand, because no means were provided to adjust all stages once and tor all to have identical electrical characteristics over the entire operating range. The inevitable result of this detuning was a serious impairment both of amplification and selectivily.

'l'here hanbeen proposed,SO-(illlGd masi(l-('(lllll()l radio-frequency receivers in which a single control is provided for the purpose of roughly tuning, simultaneously, each of several circuits, a number of separate controls being providedito tune the individual clrcuits to exact resonance, thereby overcoming the mentioned detuning which results from inequalities in the elements of those circuits. That system, of course, defeats its own purpose, since there are actually at least as many controls as there are circuits to be tuned. v i

Furthermore, receivers are frequently used with antennae improperly erected by those unfamiliar with the preferred characteristics of such structures, so that such antennae vary widely in their constants, and consequently the tuning of the circuit immediately asso ciated with the antenna system is affected within wide limits. j

One of the main advantages of this invention resides in its application to a multistage radio-frequency amplifier wherein a single control may be employed, as distinguished from the previously discussed master-control togetherwith supplemental controls for the individual stages.

The above-named advantages of this inventoin are introduced largely by virtue of the provision of a variable condenser which, in addition to the usual means for varying its electrostatic capacity, includes adjusting means whereby the minimum capacity and the rate of change of capacity of the condenser may be independently adjusted. This application is a division of my application for United States Letters Patent Serial No. 20,481, filed April 3, 1925, for unicontrol signaling system.

Referring to the drawings:

Fig. 1 shows a plan view of a radio receiver embodying this invention, with the cover of the cabinet removed;

Fig. 1 shows a front elevational View of the receiver illustrated in Fig. 1 with certain parts broken away to disclose the interior arrangement of parts;

' 1''i g. 1 shows a side elevational view of this receiver with a side. wall removed; 1 Fig. 1 shows a form of electrostatic screen utilized in the preferred embodiment of this invention rod 2. In the space of approximately 55 Fig. 1 shows the complete circuit diagram Y of the receiver illustrated in the above; 0

tube, terposing a step-up transformer, as has heretofore been the practice when external anas illustrated in Fig; 1',-instead of in Fig. 2 shows a calibration curve of aria v tennae have been employed. This connection i bl d r; a d 3-. nesultsin an increased radio-frequency grid Figs. 2 and 2show two views of apre.--potent1al, and partly compensates for the ferred construction for the variable conshortness of theantenna. With well-designed I densers, including the two adjustable fee-1 circuits and apparatus, it is possible in this Referring to Figs. 1", 1" and 1, there is shown a radio receiver cabinet with an upper compartment 5, 6, 7 and 8 within which are t a y those stations which are mounted coils T T T a multi-unit'condenser with units 0 C and C vacuum tubes V V V V an audio-frequency transformer AF, and all necessary batteries enclosed in a metal container. It will be noted that'the mentioned coils, in order to minimize undesirable magnetic coupling between them, are mounted in a row at one side'of the compartment with their axes inclined at an angle to their common line of centers. The shaft of the multi-unit condenser is mounted in bearings-supported at the front and rear of the compartment and is arranged to be rotated by a' control or pointer 26 which moves over a scale 27 on the panel or frontof the cabinet. At 25 there are shown rheostats for controlling the heating current of the vacuum tubes. The interior of the mentioned compartment may be lined with an electrostatic screen in the form of zig zag wires, such as 9, indicated in Fig. 1, and similar wire screens 9 indicated by dotted lines in Fig. 1 may be employed to partially shield the stages from each other. Each section of the screens should preferably beconnected at one point to the low-potential side of the filament circuit. This system of screens, together with the batteries and their container appearing in the upper right hand corner of Fig. 1, may, due to the resulting large conducting surface, serve as a counterpoise in the antenna system. In this way the conducting surface is made large and the rep sistance of this portion of the antenna system reduced. At the lower portion of the cabinet there is mounted a metal sheet '1, serving as an antenna, which is connected to the first tuning coil T Fig. 1 by means of a metal between the metal sheet 1 and the upper compartment, there may be supported in any convenient manner a loudspeaker mechanism i and an amplifying horn 3.

The above-described arrangement of coun-, terpoise and antenna provides an antenna system of very low radio-frequency resistance and of fairly high capacity relative to the linear dimensions, although the effective height is low. The low resistance and moderate capacity of the antenna make desirable the connection of the antenna directly to the grid of the first radio-frequency amplifying and one stage of audiothe preferred embodiment v the value v resulting in extreme simity resulting from changes in antennae are 1 negligible as compared with the resultant capacity of -the condensers; or if such antenna condenser be arranged to be adjusted once for all-with the particular antenna employed.

The details of the condenser assembly shown schematically in Fig. 1 are disclosed in Figs. 2 and 2. Referring to the latter figures, there are shown two condenser unit-s C and G each comprising a set of rotor plates 30, and interleaved therewith in the usual manner a corresponding set of stator plates 31. The rotor plates in the specific embodiment are indicated as of semi-circular configuration and are mounted upon. a rotor shaft 12, common to all condenser units for providing a uni-control tuning arrangement. The groups of stator plates 31 for each of the condenser units C and C are so assembled as to constitute distinct stator elements electrically insulated from one another. The as sembly in each case includes a group of stator lates 31 suitably mounted between end plates 16 and 37 of insulating-material, by means of the spacing members 33, nuts 34 and the screw-threaded bars 35. It will be observed that each stator assembly has a pair of insulating end plates 16 and 37 in-- The stator elements of condenser units C and G may be mounted upon a common supporting structure by any of the many arrangements well known in the art, as for example, by afiixing the insulating end plates 16 and 37 to a set of tie rods common to all of the condenser units.

The additional plates 10 and 11 associated with each condenser unit which constitute the adjustable means referred to above for determining the minimum capacities and the rate of variation in the capacities of the condenser units will be discussed below.

The member 12 is shown broken off at the dividual thereto.

. the assembly.

left of Fig. 2 to indicate that any desirednumber of additional condenser units similar to C and 0 may be similarly included in The dotted line 9 in Fig. 2 indicates' the manner in which the electrical shields or screens referred to above are. interposed between the successive condenser units.

' A'convenient and compact form of tuning condenser-is that having circular moving platesj This form ofcondenser gives within its working range a straight line relation between capacity and angular adjustment, or displacement, as illustrated in Fig. 2. To carry out the purpose of this invention, it is necessary that the; condenser plates be rigidly and accurately plane and parallel, so that the calibration curve, Fig. 2, will be identical in shape for all condensers. This curve should preferably be a straight line. However, there will' still exist the probability of differences in the various tunable oscillatory circuits, due to differences in the fixed capacitiesEof the wiring and of the coils, etc.; and there may also be variations in the clearances of the plates of the different condensers that will cause their rates of change of capacity to differ slightly from one another. To compensate for the first condition a supplemental or auxiliary adjustable plate 1O, shown in Figs. 2 and 2, electrically connected to the moving plates, but not moving with them, is placed adjacent to one of the outer stationary plates of each condenser unit and is adjusted relatively to that plate,

when the receiver is first assembled, so as to tune both radio-frequency amplifier input circuits and the detector input circuit to the same maximum resonant frequency when the main variable condenser units are set for minimum capacity.

While for the purpose of this invention adjustable plate 10 can be supported in any convenient manner, it may for example, be mounted as illustrated in Fig. 2 The construction there illustrated provides a threaded journal 13 surrounding the condenser shaft 12. On the inner end of this journal there is an integral collar 15 against which a nut 14 forces the condenser plate 10. Another nut 17 holds the journal tightly to the insulating plate 16 and serves to lock the assembly after the proper adjustment has been made.

T o compensate for the differences in the rates of change of capacity of the various condenser units, or in the rates of change of resonant frequency of the oscillatory circuits p in which the condenser units are connected an outside stationary plate 11 of each condenser unit. Fig. 2", is arranged to he moved axially. This latter adjustment is made when the receiver is first assembled so as to tune all three rzulio-frequency input circuits to the same minimum resonant frequency when the main'variable condensers'are set for maximum capacity. This adjustment may effect slightly the initial adjustment of plate 10 which may now have to be read:

usted. The final result of these adjustments is that all of the tuned circuits will be in resonance with one another for every setting of the tuning condensers, because the calibration curves are straight lines (or else are exactly similar) and, having been made to coincide at two points, coincide throughout. In other-words, the slopes of the capacity-displacement curves of the several condenser units will be substantially identical. When all the tuning condenser units are provided with these adjustable features, it is possible to. engrave a wavelength or frequency scale 27 on the panel, prior to assembly, and to permanently adjust all condenser units to suit this scale.

The adjustment-of plate 11, Figs. 2 and 2, will also compensate for accidental diiferences in theself-inductance of the tuning coils. Mechanical forms of adjustment other than those indicated in Figs. 2 and 2 are, of course, possible, but In general, they should be such as to determine or vary, first, the fixed or minimum value of the tuning capacity (or maximum resonant frequency) and second, the rate of change of capacity (or resonant frequency) with given displacement of the tuning control.

It is possible to use other shapes of confrequency amplification including the vacuum tubes V and V a detector tube-V and an audio-frequency amplifier including the tube V.,. A greater or less number of stages of radio-frequency or audio-frequency amplification may be used, if desired, without departing from the spirit of this invention. The first tuned circuit of this diagram includes the electro-static capacity of the antenna system above referred to which is not resent in the tuned circuit of V or the circuit of the detector V On the other hand, these last two tuned circuits have capacity between the primary and secondary coils of the radio-frequency transformers T and T3. which is not present in the first tuned circuit of V These two capacities will, in part, balance each other, the difference being taken lZU care of by the factory adjustments of the variable condensers, as previously described. A neutralizing condenser C connected between the grid circuit of vacuum tube V and the secondary winding of transformer T together with a second neutralizing condenser (1,, connected between the grid circuit of vacuum tube V and the secondary winding of transformer T function to eliminate undesirable inherent capacity couplings, and hence to prevent regeneration and a corresponding tendency towards oscillations.

The presence of regeneration control is incompatible with the unitary tuning control of a plurality of successive tuned stages in a vacuum tube amplifying system becauseany appreciable variation in the regeneration adjustments necessitates a corresponding variation in the tuning control of those stalges only in which the regeneration occurs. he degree of regeneration and the corresponding tendency towards oscillations is largely determined by naturally variable factors, such as the condition of batteries, i. e., the internal resistance thereof, the settings of the filament rheostats and the characteristics of the vacuum tubes, because those and other factors influence the effectiveness of the couling between the output and input circuits of the tube or tubes. It therefore follows that in order to render unnecessary the detuning of any of the stages for oscillation control and to attain efiicient simultaneous tuning of the several successive circuits every reasonable precaution should be taken to prevent regeneration. To this end 'an em odiment of the present invention is herein described as including means for neutralizing or eliminating substantially all undesired capacity coupling, electromagnetic coupling and other forms of undesired coupling, whereby regeneration is substantially prevented. It is unnecessary to describe further the functions of the various circuits since they are fully disclosed in my mentioned patents. It will be understood, however, that the tuning of the circuits of V V and V is simultaneously and uniformly accomplished since the condenser units C C and C of these circuits are controlled by the common rotatable shaft 12.

I claim:

1. In combination with a condenser whose capacity is variable by physical displacement of an electrode thereof. a first means for adjusting the capacity value at a first point of displacement of said electrode, and a second means for adjusting the capacity value at a second point of displacement of said electrode without substantially aii ecting the adjustment of capacity value at said first point.

2. In combination with a condenser whose capacity is variable by physical displacement of a movable electrode with respect to a relatively fixed electrode, a first means conductively connected to the fixed electrode for adjusting the capacity value at a first point of displacement of sa1d movable electrode, and a second means conductively connected to the movable electrode for adjusting the capacity value at a-second point of displacement of said movable electrode. v

3. In a variable condenser structure including two variable condenser units intended to have substantially identical capacity-displacement characteristics, a first adjusting means conductively connected to one of sai units for individually effecting a substantially identical minimum capacity value for both of said units, and a second adjusting means conductively connected to one of said units for individually effecting a substantially identical maximum capacity value for both of said units.

4. In a variable condenser structure comprising aplurality of condenser units the individual capacitiesof which are simultaneously variable by a unitary control which displaces an electrode with respect to another electrode of each unit, two individual means supplemental to said unitary control for at least one of said units to individually adjust the capacity of said last-mentioned unit at two different points of displacement, whereby the capacities of said units are brought into agreement.

5. A condenser unit including a displaceinent-control means for varying the capacity thereof whereby the capacity is of a first value at a first point of displacement of said control means, and of a sccond value at a second point of displacement of said control means, in combination with a second condenser unit whose capacity is also variable by the said displacement-control means, said second condenser unit being prhvided with a plurality of adjusting means supplemental to said control means whereby the capacity value of said second condenser unit may be individually adjusted to be substantially identical withthe capacity value of said first condenser unit at each of said points, respectively.

6. The combination with a condenser structure comprising a plurality of variable condenser units the capacities of which are simultaneously variable by a single control element,

variable by a single control element, of pairs of supplemental adjusting means individual to one or more said condenser units, with one adjusting means of each said pair determin- 5 ing the minimum capacity of the corresponding condenser unit and the other ad ustln means of such pair determining the rate OI variation in capacity of such condenser unit when the capacity thereof is varied by operation of said control element, whereby. the capacities of said plurality of condenser units may be brought into correspondence for all positions of said control element.

8. A variable condenser comprising three distinct capacity-ad'usting means, a first of said means being a justable to vary within minimum and maximum values the effective capacity of said condenser, a second of said means being adjustable to determine the minimum capacity of said condenser, and a third of said means being adjustable to determine the rate of variation of capacity of said condenser when the effective capacity thereof is varied by said first adjusting means.

h In a variable condenser structure comprising at least two variable condenser units, the capacities of which are simultaneously variable by a single control element, a first adjusting means conductively connected to one of said condenser units for individually adjusting the capacity value thereof when said control element is set for minimum capacity, and a second adjusting means conductively connected to one of said condenser units for individually adjusting the rate of variation in capacity of such condenser unit when the capacity thereof isvaried by said control element.

In testimony whereof I afiix my signature.

0 LOUIS ALAN HAZELTINE. 

